The present invention is concerned with an apparatus and a method of testing hermetically sealed packages, such as pharmaceutical pill packs of the type which have metal foil or metallic laminate in the material of the package.
It is desirable for pharmaceutical pill packs to be hermetically sealed. The current practice is for audit tests to be performed during the packaging process to determine that the packaging has been properly carried out. Such audit tests involve dipping the packs in liquid methylene blue dye and evacuating the system. Any leaking packs fill with dye so that they can be identified by eye and removed manually by an operator. All packs which are tested are destroyed and the process is also very slow and messy.
It is an object of the present invention to provide an improved method and apparatus for testing the hermetic integrity of packages, in particular packages of the type which have a metal foil or metallic laminate in the material of the package.
The method of testing adopted in the present invention relies on the property of flexible sealed packages to expand when placed in a partial vacuum. If, however, the package leaks under these conditions then the air is expelled from within the package and the package will not expand as much as a properly sealed pack.
In accordance with a first aspect of the present invention there is provided a method of testing flexible sealed packages of the type wherein the packing is at least partially made of an electrically conductive foil or metallic laminate, wherein the capacitance between the conductive foil or metallic laminate of the package and a fixed electrode is measured when the package is subjected externally to a partial vacuum.
In some cases, the measurement of capacitance under vacuum conditions can be compared to the measured capacitance under atmospheric conditions, a predetermined increase of capacitance being indicative of an acceptable package seal.
In other cases, where the spacing between the various components is preset, a meaningful test can be made by absolute measurement of the capacitance under vacuum conditions alone.
In accordance with a second aspect of the invention, there is provided an apparatus for testing flexible sealed packages of the type wherein the package is at least partially made of an electrically conductive foil or metallic laminate, the apparatus comprising an evacuable chamber adapted to support a package under test therewithin so that at least part of said foil or metallic laminate portion of the package lies opposite a fixed electrode in the chamber, and means for monitoring the capacitance between said electrode and that part of the foil or metallic laminate when the chamber is evacuated.
For use in connection with a blister pack type of package having a plurality of individual compartments or "blisters", there can be a corresponding plurality of said electrodes in the chamber and a multiplexing arrangement whereby the capacitance between the foil portion corresponding to each blister and a respective one of said electrodes can be monitored.
Measurement is conveniently made using a capacitance bridge.
It is not essential to make electrical connection direct to the foil or metallic laminate itself for the purposes of capacitance measurement. Blister packs normally have one side made of an electrically nonconductive plastics material. If a further fixed electrode is then disposed beyond the plastics side of the pack, then a series capacitance arrangement is obtained with a first (fixed) capacitor being effectively formed between the further electrode and the foil and a second (variable) capacitance being effectively formed between the foil and the first-mentioned electrodes.